1. Field of the Invention
The present invention relates to a banknote processing apparatus and a banknote processing method for checking degree of soiling for various kinds of banknotes issued by a plurality of countries.
2. Description of the Related Art
Conventionally, irradiating a paper sheet with a visible light, and determining the degree of soiling of a paper sheet based on an image data of the paper sheet obtained by reflected light received from the paper sheet is a known technology. For example, Japanese Patent Application Laid-open No. 2010-277252 discloses the following technology in which visible light is irradiated on a paper sheet, an image of the paper sheet is obtained by receiving the reflected light from the paper sheet, and the degree of soiling is determined by comparing, for a low-contrast and bright area selected beforehand for checking the degree of soiling, a reference value calculated beforehand for a reference paper sheet based on a pixel value of area of the standard paper sheet of the same type for detecting a degree of soiling and an evaluation value calculated based on a pixel value of the target paper sheet to be checked. The degree of soiling of a banknote can be determined by applying the technology disclosed in Japanese Patent Application Laid-open No. 2010-277252 to a banknote processing apparatus.
However, often there is inconsistency between the results of checking the degree of soiling of the banknote by the banknote processing apparatus that employs the technology disclosed in Japanese Patent Application Laid-open No. 2010-277252 and that of visual observation of the degree of soiling. Furthermore, often a different checking result is obtained each time even if the degree of soiling of the same banknote is checked plural times by the banknote processing apparatus to which the technology disclosed in Japanese Patent Application Laid-open No. 2010-277252 is applied. It is also difficult to determine the degree of soiling of a large variety of banknotes issued by several countries on one unit of the banknote processing apparatus to which the technology disclosed in Japanese Patent Application Laid-open No. 2010-277252 is applied.
The inconsistency with the visual perception of degree of soiling checking result and variation of results of the checking of degree of soiling performed for the same banknote plural times would engender a feeling of distrust toward the banknote processing apparatus to the apparatus users. In a banknote processing apparatus intended to be used in overseas market, an identifying soiling needs to be performed for a large variety of banknotes issued by several countries. To make a banknote processing apparatus realize that the apparatus users can rely on and that can be used for overseas market expansion, it is important that the result of the degree of soiling checking by the apparatus is consistent with that of the visual perception of the degree of soiling, the variation of the results of the degree of soiling checking for the same paper sheet multiple times is reduced, and the banknote processing apparatus is capable of performing the degree of soiling checking for a large variety of banknotes.